Friday, December 01, 2006

The Permian Extinction: What Caused the Great Dying?

The Permian Extinction is one of the most profound changes to the ecosystem or life has seen at all ever. Life changed. Not merely with respect to the various species that were alive, but how the ecosystem was organized. The trends that had been pretty consistant in the Paleozoic were completely dumped. it was as though someone had come in and hit the HUGE reset button on the earth's lifeforms and their habitat.

In the process, it seems that somewhere between 60 - 90% of all living species - dependng on who you believe - went extinct during the Permian Triassic Extinction. The previous extinctions were nothing in comparison. People in the not too distant past used to point to the Cambrian Explosion (and subsequent extinction?) has the most profound impact. That extinction is lessening in magnitude with each passing year of research. There are now some paleo types suggesting there wasn't even an extinction event at all. However, that's another topic. The Permian was profound. It freed the waterways from the amphibians. It set in motion the events that led to the Age of Dinosaurs. It even set about events that led to the cynodonts becoming true mammals and thus led to you and me. There will be another post, another time for discussing the End Permian Ecosystem. This post will discuss the causes of what happened. It's not as simple as the most studied mass extinction either (the KT Event).

What were the theories about what caused the mass extinction? Well, there were a few. The longest reigning one was that the oceans receded to very low levels. The second theory that went along with the first theory was that because all the continents had come together into Pangaea, life that had been confined to certain parts of the world were not able to spread all over causing greatly increased competition and associated die-offs (the NorAm/SoAm exchange of animals due to the Panama Straits closing was the source of this theory). The next big theory was what people expected to see after investigating the KT Event: a bollide impact. The next theory was that the volcanos did it: the Siberian Traps to be specific. There have been other extinction theories that have eben related to environmental degradtion. Douglas Erwin once suggested that it was the Midnight Express: a little bit of everything did it because it it would take a lot to do such damage.

It seems that the cause was pretty straight forward after digging through the data. A concensus has grown and a theory has been largely adopted by those studying the event. Unfortuntaely, it deals away with the ide that a single source would be the cause of mass extinctions. You could not point to the sky and say if we cleaned out all the asteroids and comets that we wouldn't face another mass extinction. There is no One True Cause. All the evidence points away from a bollide impact. Rather the whole thing seems to have been kicked off by vulcanism. More properly, those evil Siberian Traps. However, it is a pretty complex chain of events that lead from there to there and a lot of explaining to do.

First off, there were actually two events at the end of the Permian. There was one that was ten million years before the second. The kill ratio was some 20% of life took a hit. That's pretty hefty. It's not as hefty as what following. Life seemed to be recovering pretty well, if the fossil evidence can be believed. Then came a long, long dying that seemed to almost end life on Earth.

What caused the long dying seems to a complex operation as to what happened. The root cause was the Siberian Traps. They belched lava and carbon dioxide over nearly a million years. The amount of lava they belched has no parallel. Not even the Deccan Traps come close. The important part was the CO2 though. It apparently was enough to warm the planet 5 degrees C above what it was already: which was already warmer than now by a considerable bit (a few degrees C).

From there, the oceans warmed. This had two effects. The oceans of the Permian seem to have been very stratified. That is to say that the oceans did not intermix from the bottom depths to the ocean surface. There were very distinct layers. Additionally, as the world warmed, the ice caps melted. This decreased the salinity of the top waters and made the stratification worse. This caused the bottom of the ocean to be anoxic (ie very little or no oxygen dissolved in the various layers). The warming made the anoxic conditions worse. Warm water holds less oxygen than does cold. Life in the water would be...less than comfortable. With the melting of the very extensive ice caps, the oceans would rise and the anoxic layers would be brought up to depths that would originally have been habitat for the Permian marine organisms (This is Hallam's regression-transgression-anoxia theory).

Then the warmed ocean unleashes a nasty surprise for the surface and atmosphere: we get methane hydrate burps. There is a large amount of methane sequestered in the ocean in the form of ices. When the water warms too much, the methane is released from the ice. This makes it way into the atmospehre. Methane is a much better greenhouse gas than carbon dioxide. This ended up causing a further 5 degree C atmospheric rise. This happened very quickly and helped to pummel the End-Permian lifeforms even more. If the simulations (PDF) of Jeff Kiehl and Christine Shields of NCAR hold up to the fossil record, this means that the methane in the atmosphere end up whacking the ozone and unleashes a lot of normally blocked ultraviolet light [here too] above and beyond the norm which helps kill off the terrrestrial ecosystems as well.

As if to add insult to injury, the hypoxic-anoxic oceans encouraged growth of anaerobic bacteria that produce lots of hydrogen sulfide. Hydrogen sulfide is nasty stuff and highly toxic. It would help kill even more in the oceans than even oxygen deprivation would. It would, futhermore, bubble out of the oceans and kill right and left anything that took a whif on land. However, to make things even worse, Kiehl et al state that it increases that length of time that the methane remains in the atmosphere. This increases the amount and heating and away we go.

In the end, what killed life at the end of the Permian? It was a negative feedback that in effect, even in such a hellaciously hot climate (72 C at the equator!), snowballed. If ever there was a time that we, the planet Earth, was dangerously close to tripping over the edge into a run away greenhouse, that would have been it. Not the Eocene. The mechanisms that regulate the CO2 content in the atmosphere broke down, got depressed, and nearly shot itself in the head; in effect nearly ending all life.

To me, based on all the evidence that's coming in about the PT Extinction, it seems that what happened is pretty settled. Details and refinements need to be done. We're a long ways from being able to close the book, say it's been written, and that we completely understand why life nearly died then. We are far closer and the alternative scenarios are, with the pace that the supporting science for the above theory is growing, falling further and further behind.

The new question, that probably ought to be asked sometime in the next decade is not why life died at the PT Extinction, but rather:

Why did it survive at all?

After all, if the carbon cycle choked and died, how did it get restarted? It looks like in the case of Venus, it didn't and that world died. Why did it not here? Perhaps a hint is in Erwin's book, Extinction, where he states that a colleague of his noticed that the fossils that people have been attributing to the 'fungal spike' looked a lot more like algae fossils to him. Perhaps the humblest of photosynethesizers saved us all. That's a bit of research for people in the future to determine though.

Next time out on the PT Event will be discussing the land ecology. Why was this event so important to us?

14 comments:

Was the survival of all life in question? because there would still be the biomass in extremophile environments, which would likely survive until the necessary water was cooked off from the crust -- which might be a very long time indeed.

And because DNA between microbial species transfers easily, even if all types of photosynthetic life were somehow killed, it's entirely possible that enough of their genomes would survive and rapidly be selected for given any not-entirely-worst-case scenario.

(All photosynthetic pathways have elements which can be reconfigured for other useful cellular purposes -- they're largely electron transfer and/or ion pump modules anyway. Even the photoreaction centers could be retooled for other purposes[rhodopsin, the chlorophylls, etc.])

"which would likely survive until the necessary water was cooked off from the crust -- which might be a very long time indeed."

Yeah, but in that case we're talking about bacterial life trapped inside the crust of a slowly cooking planet. The denouement might be delayed some hundreds of millions of years, but it's still not a happy.

"it's entirely possible that enough of their genomes would survive and rapidly be selected for given any not-entirely-worst-case scenario."

This is an interesting what-if: a Permian extinction that wipes out everything above the level of microbes, but from which the microbes then rebound. (Microbes here including eukaryotes.)

What then? Well, multicellular life has evolved a bunch of times. But large, morphologically complex multicellular life, only three times. And OTL it took some hundreds of millions of years to get from the urmetazoa to the Cambrian Explosion.

Will, a question: how did the planet recover after the event? What scrubbed the C02 out, and when/why did the oceans return to normal? Do we know?

"This is an interesting what-if: a Permian extinction that wipes out everything above the level of microbes, but from which the microbes then rebound. (Microbes here including eukaryotes.)"

[Briefly considers a TL for shwi in which the mobile heterotrophs are all fungi, gives up when it becomes apparent the borders of my ignorance about basic fungi biology are expanding faster than I am learning stuff about them]

The extremophiles would probably make it through. Everything involved in the aerobic cycle (is that the term?) would have died and after we went into the RAGH, we'd have lost the anaerobics too (sans extremophiles). I'll concur with Doug here on the rest of the story.

Carlos also spake:

Might it be possible that what prevented the Earth from going through a runaway greenhouse effect was simply the diminished insolation of that period?

Insolation? Or luminosity? I think that it would be the latter, actually, if it's either. The insolation was actually higher than now if I don't misunderstand the work written.

Doug then said:

Will, a question: how did the planet recover after the event? What scrubbed the C02 out, and when/why did the oceans return to normal? Do we know?

AFAIK, no one's touched that question at all. I brought it up because we seem to have wrapped our head around the extinction, but not the recovery. Mass Extinction Recovery Studies, as I understand it, are even younger than mass extinction studies. This one's important I think especially since its a very multidiscplinary study to figure this one out.

Insolation should track luminosity -- it's per area, with sometimes an angle factor.

The Sun's luminosity IMS has been increasing with time. (Noel and I got in a discussion about this once, and we killed an hour trying to work it out from first principles. I wish I could remember what we concluded. Anyway, Google agrees.)

Question: is a runaway "boil the oceans" greenhouse possible on Earth with current levels of insolation? Knowing that would bracket the Permian outcome.

(Wikipedia says that water on Earth is significantly lower than the critical positive feedback level -- 30% to 40% -- but it also says 'citation needed', so I don't know quite what it's referring to.)

Thanks for a post about the Permian. It's a big obsession of mine. I read almost all of the literature about it.

As to the cause... I wonder why everyone discounts a possible meteor/asteroid impact as the first cause which led to the massive volcanism. If they don't think an impact did it, how do scientists account for this volcanic upsurge? Sure, volcanism is part of the Earth's normal behavior, but the Siberian Traps seem way out of line. Plus, is Siberia at the edge of a tectonic plate, where volcanism usually occurs?

I just don't understand why there is this assumption that NO, Earth's most severe catastrophe wasn't caused by an impact (which is very common in space, every other planetary body is covered with craters) but it just sort of "happened" because things got bollixed up on the Earth.

Duh???

Then there was a news story about a giant impact crater beneath the ice of Antarctica. Nobody has commented on that. Why not?

It's way easier for me to believe that a giant bolide could "crack" the Earth and let the magma well out...than to believe it just happened all by itself.

1st: Then there was a news story about a giant impact crater beneath the ice of Antarctica. Nobody has commented on that. Why not?

Because there's no supporting evidence. The problem with a PT boundary impact is that all the evidence that made the KT Boundary a slam dunk for an impact is completely lacking. There's no sign of spherules save at Antarctica itself. There's no sign of any impact effects the world over and a bollide the size necessary to cause the PT extinction would be MUCH larger than the KT Impact. The evidence should be even MORE visible the world over even if it lacked iridium. Yet...it's not there. Or even hinted at anywhere save perhaps one site. That hurts the impact hypothesis pretty bad.

2nd question: As to the cause... I wonder why everyone discounts a possible meteor/asteroid impact as the first cause which led to the massive volcanism. If they don't think an impact did it, how do scientists account for this volcanic upsurge?

Again, no supporting evidence. So far. IDK how much people have been looking at this though. There's been a bunch trying to drum up support for the Deccan Traps having been impact intiated - that Shiva 'Crater' - but as yet I don't think anyone has been out doing the field work for the Siberian Traps. However, I am guessing that there ought to be plenty of evidence again world wide...that'd be a major impact! Yet again...

There are some plausible hypotheses for the Traps iniation besides extraterrestrial - superplumes frex - but they are very tenative at this point due to the very fact that there are soooo few eruptions on this scale.

A comment to a comment. someone answered my comment about bolide evidence, saying there wasn't any 'slam dunk' evidence like at the KT. (worldwide iridium levels, spherules etc.)

Yeah, but from what I've read, there is very little surviving geologic material from that layer because most of the Earth's crust has been recycled since 250 mya. So... the evidence has been destroyed. There isn't going to be any slam dunk.

Yeah, but from what I've read, there is very little surviving geologic material from that layer because most of the Earth's crust has been recycled since 250 mya. So... the evidence has been destroyed. There isn't going to be any slam dunk.

You are correct in that a lot less sections from that time period are around. It's just the nature of the geological beast we sit on.

However!!! had there been the same number of KT Boundary sections as there are PT Boundary sections we would have still had a slam dunk. There are a number of PT boundaries "lying" around (China - where they put the 'Golden Spike' btw, Greenland, the Karoo, Nevada, Antarctica, the Alps, etc.) that there ought to have been something at each, especially with the size of the crater that would have been required.

There's zip. Nada. Nothing.

There was a report of shocked quartz from Antarctica. That was retracted.

There is, however, a lot of evidence that the world was being baked and seared by a nasty cocktail at the time. An overwhelming amount of evidence right now. There are other extinctions that it looks as though impacts may be the cause -Devonian is a hot potato right now on the subject - but this one is pretty much settled.

it is because of the siberian traps (a extinct chain of volcanoes) spewing carbon dioxide and causing global warming which in turn cuase the oceans to heat up causing the oxygen to leave the water and producing a bacteria which produced hydrogen monoxide a toxic gas that bubled out of the oceans and killed everything except 5% pf all life.

It is conceivable that the Siberian traps arose by virtue of crust disruption at the antipode of a meteorite impact. I suspect that you will find interesting a hypothesis that most of the large lava flows on Earth and Mars result from disruption of the crust at the antipode (opposite side of a sphere) from a huge meteorite impact. You may see it discussed in http://charles_w.tripod.com/antipode.html for Earth and http://charles_w.tripod.com/dweber/mars_volcanos/mars_volcanos2.html for Mars. The chance that there would be a lava flow at the antipode of each of the large known meteorite impact sites of the same age by sheer coincidence is extremely small.. Sincerely, Charles Weber

Its possible, Charles, but at the moment seems to be unlikely. The impact which would have set off the Siberian Traps would have been more than enough to trigger an incredible mass extinction in and of itself. The Hellas Impact was far, far more powerful than anything we have record of here on earth since at least the Archean.

Will, wonder if you - or anybody - could guide me to some free online images of stem-mammals. Do museums have accessible photos, sketches? Most of the stuff I see is either anatomically incorrect or, if correct, boring. It's for a FB album on Synapsid Evolution. No big deal but would appreciate sincerely any help. Most searched for at moment: cynodonts